1. Ph.D. Student, Dept. of Civil and Environmental Engineering, Utah State Univ., Logan, UT 84322.
2. Professor, Dept. of Irrigation and Reclamation, Faculty of Agricultural Engineering and Technology, College of Agriculture and Natural Resources, Univ. of Tehran, Tehran Province, Tehran, District 16, Azar St., Sq., Enghelab, Iran (corresponding author).
3. Professor, Dept. of Geography, Univ. of California, Santa Barbara, CA 93106.